Production of plates for printing in lithographic manner



Patented May 7, 1940 ,.-1LITHOGRAPHIC MANNER- William H. Wood, Bedford, ".ohiofassignorfl to flarris-seybold Potter Company, Cleveland,

Ohio, a corporation of Delaware No Drawing. Application June 18, 1937,

. Serial No. 148,983

23 Claims. (01. sis-5.4)

The present invention, which relates as indicated to the production of plates for printing in the lithographic manner, involves in the first place the use of a new and improved coating material for such plates, The inventiomalso has in view improvements in various of the other materials and successive steps required to prepare a plate thus coated for printing and to maintain it in proper condition for printing. Certain of these other materials and improved steps are new in the art, their use being rendered possible by reason of the employment of such improved coating material, while others are adaptable for use both with such improved coating and other coatings at present in use.

In common methods of preparing plates for lithographic printing, the plate, usually of zinc or aluminum, is coated with a water solution of a1- lbumi'n which has previously been made sensitive ito the action of light by the addition of a sensitizing agent such as ammonium chromate or dichromate. After the plate has been coated and allowed to dry, it is exposed to light in the form of an image of the subject which is to be printed. The light hardens the albumin coating to the solvent action of water, thus forming a reproduction of the subject in hardened albumin and leaving the remaining portions of the albumin coating relatively unhardened. A suitable developing ink is applied to the coating and then the unhardened areas are removed by dissolving them away with water. After application of an etching solution to clean the non-image portions of the ;plate and render them receptive to water, the plate is' in condition for printing.

' The above, process, which is in common use, is subject to numerous disadvantages and limitations, chief. among which are: (1) non-uniformity of different albumin coatings as regards their sensitivity to light; (2) variation in sensitivity of the same coating to light with the elapsed timehbetween coating and exposure; (3) rapid deterioration of the albumin coating solution and ofthe coating after application to the plate; (4) large variation of sensitivity to light with variationsin humidity and temperature conditions; (5) shortlife on the press because of low mechanical strength and lack of resistance to the etching materials used in the dampening solution; (6) limitation of the sensitivity of the albumin coatings to the violet and ultra-violet portions 01' the spectrum of light sources used for exposure; and (7) the necessity for intense sources of'illumination and relatively long exposure times in order to produce satisfactory results.

As above indicated, one object of the present invention is to provide an improved material for use in coating lithographic plates, one which will reduce, if not entirely obviate, the difiiculties just noted as inherent in the familiar albumin coating. A further object is to provide new and improved steps in the treatment of lithographic plates, particularly where coated with my new and improved material, whereby not only is a plate obtained having superior printing qualities,

but one which is mechanically stronger and at the same time more resistant to the etching materials used in the dampening solution.

To the accomplishment of the foregoing and related ends, said invention, then, consists of the steps and ingredients hereinafter fuly described and particularly pointed out in the claims, the

following description setting forth in detail certain steps and product exemplifying my invention, such disclosed procedure and product constituting, however, but one of various applications of the principle of the invention.

In general the present improved process involves the steps of coating the plate, preferably of metal or having a metallic surface, with a suitably sensitized colloidal material comprising halogenated polyvinyl alcohol or a reaction product thereof or a mixture of either of these with a water, alcohol, or alkali soluble protein material; sensitizing the coating material, either before or after coating, to the action of light, printing thereon an image by means of light; and subsequently rendering the image portions of the plate ink-receptive and the non-image portions water receptive or ink repellent.

In the general process as above outlined, the steps subsequent to the coating of the plate may be carried out by the use of'materials and methods commonly used in the preparation of plates light-printed image of a developing ink containing as essential ingredients aryl-aliphatic ketones and fatty acid amides or amines; the development of the image by means of an aqueous solution of glucono-delta-lactone or gluconic acid; and the subjection of the developed image to a heat treatment which resinifies the image material making it water, acid and alkali proof and bonding it to the metal base. This heat treating step also increases the ink receptiveness of the image to a remarkable degree.

Vinyl alcohol or ethenol (CH2:CH.OH) occurs in commercial ether, but has not yet been isolated (B. 22, 2863). However, polyvinyl alcohol is now commercially available and I have found that the product obtained by reacting on such polyvinyl alcohol with a halogen, preferably chlorine, (bro- 'mine or iodine also yield a satisfactory product),

may be readily dissolved or dispersed in water. Such solution, the term as here employed connoting either a true solution or a fine colloidal suspension, may then be applied to the surface to be treated and upon evaporation of the solvent or vehicle, a film of the halogenated polyvinyl alcohol is deposited as a uniform coating.

The actual formula of polyvinyl alcohol is not definitely known, but may be represented as So far as I am aware, it has not been definitely established whether the halogen is added at the ends of the chain or whether it replaces one or more of the side-attached hydrogen atoms.

Commercial polyvinyl alcohol comes in the form of a white dry powder, but the viscosity in a given water solution, e. g., a 3% solution, varies, corresponding with what is termed a low, medium and high viscosity product. Presumably the difference in viscosity is attributable to differences in the degree of polymerization of the alcohol. My improved halogenated derivative may be made from the polymerized alcohol, irrespective of the degree of polymerization. Both the chlorinated and brominated derivative in dry I form is a fine white granular powder readily dissolving in water degrees C. to give a white iridescent solution, dissolving more slowly at lower temperatures.

Instead of using simply a water solution of a halogenated polyvinyl alcohol for application to the plate, such alcohol is preferably dissolved in a water solution containing the halogen corresponding to that used in halogenating the alcohol or its derivative or in a solution of the halogen hypo-acid corresponding to the halogen used in halogenation. Thus, for example, in the case of the chlorinated polyvinyl alcohol, this may be dissolved in a water solution of hypochlorous acid. The resultant coating when such solution is applied to the plate is not only immediately more resistant, but such coating becomes tougher upon exposure to light and also may be more readily hardened by heating as hereinafter described.

In coating the plate with the colloidal solution of halogenated polyvinyl alcohol, or derivative thereof, it has also been found desirable to add a water soluble surface tension depressant, the Purpose of which is to enable the colloidal solution to flow into surface irregularities of the plate and form a continuous surface-contacting coating, Suitable materials for this purpose are propyl alcohol, butyl alcohol, or a sulphated higher alcohol or sulphonated oil of the type commercially available as Erkalin. While excellent results may be obtained under certain conditions without the use of a surface tension depressant, the addition of such material constitutes an important improvement in the process.

For rendering the coating sensitive to the action of light, the sensitizers common to the art such as ammonium chromate or dichromate may be used. In addition to these certain organic chromates and dichromates may also be used. For example, the reaction product of a quaternary ammonium hydroxide and chromic acid or ethylene diamine and chromic acid or a soluble dichromate. Such organic sensitizing agents are advantageous in that they show less tendency to crystallize and hence produce a more uniform sensitized coating. Chromic acid alone can also be used as a sensitizer and under certain conditions it is the preferred one. It is a fact known to the art that chromic acid cannot be used as a sensitizing agent with albumin, gum arabic or glue which substances are those commonly used in known methods of preparing lithographic plates.

The manner in which the sensitizing agent is applied to the coating material may be varied. It may consist in the addition of the sensltizer to the colloidal material forming the coating prior to the coating process or it may consist in bathing the coated plate in a solution, for example, an alcohol solution, of the sensitizing agent. The sensitizing of lithographic plates by bathing them after coating, rendered possible by the use of the present improvements, is an important advance in the art since it enables plates to be coateda considerable time or shipped some distance prior to use.

After the plate has been coated with the sensitized colloidal material or has been coated and subsequently sensitized, it may be exposed to the action of light in the usual way to harden the image portions of the coating to the solvent action of water or other developing agent. Important differences are, however, apparent as compared to plates coated with albumin; namely, the plate is much more sensitive to the light of the usual sourcesof illumination, such as carbon arcs and consequently a very much shorter exposure time is required. Furthermore, the plate is sensitive to a wider range of wave lengths of light with the result that variations in the color of the light source due to sputtering or variation in the length of arcs have much less effect on the plate.

While common developing inks can be used in carrying out the process in its broad aspects it or a fatty acid amide or amine such as stearyl amide or amine or both. This is a radical departure from the previous art and constitutes one feature of this invention. The particular advantages resulting from the use of this type of developing ink are: (1) The ink has great penetrating power for halogenated polyvinyl alcohol coating thereby incorporating itself throughout the thickness of the coating so thoroughly as to be removed only with great difliculty. (2) The coating is made highly ink attracting with the result that a relatively large quantity of ink can be carried by and removed from the plate during printing. (3) The coating is rendered more water proof and acid proof.

For dissolving off the unexposed portions of the coating, warm water may be used as is the common practice with albumin plates, but the use of warm water in connection with the process herein described has the objection that not all the unexposed material is removed unless development is very prolonged. In order to remove the unexposed portions completely so as to leave the printed image intact and yet not attack the metal of the plate, it has been found preferable to use an aqueous solution of gluconic acid or glu-' cono-delta-lactone This may be a -50% solution by weight of either the acid or the lactone in water. Either of these solutions possesses high solvent power for the dry unhardened colloid used as a coating. This use of a moderately weak organic acid for developing purposes is a new and improved step in the art and constitutes a further feature of this invention. Solutions for such use in the known procedures for making lithographic plates are either alkaline solutions or solutions of strong mineral acids.

After development of the image by dissolving away the unhardened portions of the coating, it is possible to employ the plate for printing without further treatment. Superior and highly advantageous results are obtained, however, by subjecting the developed image to a heat treatment and this step constitutes a further improvement in the invention. Various degrees of heat supplied for varying lengths of time may be employed, it being true in general that the lower the temperature, the longer the time required to obtain a given result. It is also true that some improvement in the image material is obtained simply by prolonged aging at ordinary room temperatures. It is preferred, however, to resinify the image material to make it completely resistant to water and acids and alkalies of a concentration weaker than those which would destroy the metal plate, and to this end, when zinc or aluminum is used as the material of the plate, it has been found sufl'lcient to heat the plate to 100 C. to 130 C. for to 30 minutes. For other metals it is possible to employ higher temperatures and consequently shorter times without harmfully affecting either the plate or the image material. At the temperature just mentioned there is little or no hardening of albumin and an image of protein material remains sensitive to dilute acids and alkalies; there is no resinification such as is obtained when the halogenated polyvinyl alcohol is heated. Furthermore, a firm bonding of the image material with the metal results on heating as is proved by the fact that the image can be removed only by grinding away the image substance with an abrasive or by destroying the metal plate with a concentrated mineral acid.

I have found that acrylic acid or certain alkylated derivatives thereof, such as alpha-methyl-acrylic acid or their salts polymerized in such a way as to be water soluble, by which term is also connoted such a compound in water-dispersible form, all provide an excellent agent or medium to be applied to the non-printing portions of such lithographic plates, making such portions water attracting and highly ink repelling. An agent or medium having the composition just described is equally effective and desirable for application to the plate prior to the printing operation and as a dampening fluid to be fed to or applied to the plate during the printing operation. Where used as a dampening fluid, the agent in the form of a solution or dispersion may be fed to the plate in any known manner.

The concentration of the polymer or its salts, whether applied to the plate directly in preparing the same for printing or by means of the water fountain during the printing operation, is not critical, but concentrations of from 1 to 10 per cent. are ordinarily suflicient. For certain types of printing where excessively greasy inks are em ployed, it'may be desirable to combine with such polymer a mild organic acid, such as the gluconic acid or glucono-lactones previously mentioned, or pyruvic or levulinic acid,

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims,

or the equivalent of such, be employed.

I therefore particularly point out and distinctly claim as my invention:

1. In the preparation of plates for printing in the lithographic manner, incorporating a watersoluble halogenated polyvinyl alcohol and additional halogen the same as that of the compound in a solution, and applying such solution to the plate.

2. In the preparation of plates for printing in the lithographic manner, incorporating a halogenated polyvinyl alcohol and a hypo-acid of the same halogen as that of the compound in a solution, and applying such solution to the plate.

3. In the preparation of plates for printing in the lithographic manner, incorporating a halogenated polyvinyl alcohol and a water-soluble surface-tension depressant in a solution, and applying such solution to the plate.

4. In the preparation of plates for printing in the lithographic manner, providing the plate with a coating of a halogenated polyvinyl alcohol light-sensitized by the action of chromic acid.

5. In the preparation of plates for printing in the lithographic manner, providing the plate with a coating of a halogenated polyvinyl alcohol light-sensitized by the action of a chromium compound, exposing the plate to light in desired areas to obtain an image, and treating the coated surface with a developing ink,

6. In the preparation of plates for printing in the lithographic manner, providing the plate with a coating of a sensitized halogenated polyvinyl alcohol, exposing the plate to light in desired areas to obtain an image, and treating the coated surface with a developing ink.

7. In the preparation of plates for printing in the lithographic manner, coating the plate with a sensitized halogenated polyvinyl alcohol, exposing the plate to light to obtain a desired image, and treating the coated surface with an aryl-alkyl ketone.

8. In the preparation of plates for printing in the lithographic manner, coating the plate with a sensitized halogenated polyvinyl alcohol, exposing the plate to light to obtain a desired image, and subjecting the coated surface to the acion of a moderately weak organic acid.

9. In the preparation of plates for printing in the lithographic manner, coating the plate with a sensitized halogenated polyvinyl alcohol, exposing the plate to light to obtain a desired image, and subjecting the coated surface to the action of gluconic acid.

10. In the preparation of plates for printing in the lithographic manner, providing the plate with a coating of a halogenated polyvinyl alcohol light-sensitized by the action of a chromium compound sensitizer, exposing the plate to light in desired areas to obtain an image, and treating the. surface with a developing agent to remove portions of the coating.

11. In the preparation of plates for printing in the lithographic manner, providing the platewith a coating of halogenated polyvinyl alcohol light-,

the plate to light in desired areas to obtain an sensitized by a chromium compound, exposing image, developing the image contrast, and subsequently heating the plate.

12. In the preparation of plates for printing in the lithographic manner, coating the plate with a halogenated polyvinyl alcohol, treating the coated surface with a chromium light-sensitizer compound, exposing the plate to light in desired areas to obtain an image, and treating the coated surface with a developing ink.

13. In the preparation of plates for printing in the lithographic-manner, coating the plate with a halogenated polyvinyl alcohol, treating the coated surface with chromic acid, exposing the plate to light in desired areas to obtain an image, and treating the coated surface with a developing ink.

14. In the preparation of plates for printing in the lithographic manner, coating the plate with a halogenated polyvinyl alcohol, treating the coated surface with a bath of an organic salt of a chromic acid, exposing the plate to light in desired areas to obtain an image, and treating the coated surface with a developing ink.

15. In the preparation of plates for printing in the lithographic manner, coating the plate with a halogenated polyvinyl alcohol, treating the coated surface with a bath of a chromium compound from the group consisting of chromic acid and an organic salt of a chromic acid, exposing the plate to light in desired areas to obtain an image, and treating the coated surface with an aryl-alkyl ketone.

i 16. In the preparation of plates for printing in the lithographic manner, coating the plate with a halogenated polyvinyl alcohol, treating the coated surface with a bath of a chromium compound from the group consisting of chromic acid and an organic salt of a chromic acid, exposing the plate to light in desired areas to obtain an image, and treating the coated surface with a higher fatty acid amide.

17. In the preparation of plates for printing in the lithographic manner, applying to the plate a halogenated polyvinyl alcohol and subjecting the polyvinyl alcohol to the action of a light 2,199,866 sensitizer, exposing the plate to light in desired areas to obtain an image, applying a developing ink and subjecting the surface to the action of a moderately weak organic acid.

18. In the preparation of plates for printing in the lithographic manner, providing the plate with a coating deposited from an aqueous solution containing a halogenated polyvinyl alcohol and a water-soluble surface-tension depressant, and in the presence of a light sensitizer exposing the plate to light in desired areas to obtain an image, treating the coated surface with a developing ink, subjecting the coated surface to the action of a moderately weak organic acid, and subsequently heating theplate. 1

19. In the preparation of plates for printing in the lithographic manner, coating the plate with an aqueous solution containing a halogenated polyvinyl alcohol and a hypo-acid of the same halogen and a water-soluble surface-tension depressant, treating the coated surface with an organic salt of a chromic acid, exposing the plate to light to obtain a desired image, treating the coated surface with an aryl-alkyl ketone, then subjecting to the action of gluconic acid, and finally heating the plate.

20. As a new product, a plate having a surface evaporation-deposited from a water solution of a halogenated polyvinyl alcohol containing additional halogen the same as that of the halogenated polyvinyl alcohol.

21. As a new product, a plate having a surface evaporation-deposited from a water solution of a halogenated polyvinyl alcohol and light sensitized by chromic acid.

22. As a new product, a plate having a surface of halogenated polyvinyl alcohol with areas changed by exposure to light and an aryl-alkyl ketone developing ink.

23. As a new product, a plate having a surface of halogenated polyvinyl alcohol with areas changed by exposure to light and a higher fatty acid amide.

WILLIAM H. WOOD. 

